This invention relates in general to sealing shafts and the like and more particularly to a seal and shielded seal assembly.
A type of antifriction bearing, known as an all-purpose bearing, exists which is furnished as a sealed self-contained assembly that is preset and prelubricated. As such, the bearing is simply fitted over an axle journal and into a housing to enable the axle to rotate relative to the housing or vice versa. All-purpose bearings have experienced wide-spread use on axles of railway cars, but they are also used in other applications, such as for crane wheels, table rolls and shears, and even for the work rolls of rolling mills.
All-purpose bearings often operate in hostile environments, and this is particularly true when they are used at the journals of railway cars. Here they are subjected to contaminants, such as moisture and road grit, which must remain out of the bearing interiors to prevent premature failure of the bearings. Hence, the presence of seals at the ends of all-purpose bearings.
The typical seal for an all-purpose bearing has a seal case which is fitted to the outer race of the bearing and an elastomeric seal element which is bonded to the seal case and bears against a wear ring at the end of one of the inner races for the bearing. Actually, the seal element contacts the wear ring at two axially spaced locations, namely along a primary lip that is on the so-called oil side of the seal and also along dust or secondary lip that is on the air side. A garter spring encircles the primary lip to urge it snugly against the wear ring, where it is supported on a thin, yet continuous, film of lubricant, known as an elastohydrodynamic oil film. The dust lip likewise bears against the wear ring, but merely under the bias of the elastomer from which the seal element is molded. The primary lip establishes a very effective barrier to the migration of the lubricant along the wear ring--so effective that it is not uncommon for the dust lip to starve for lubrication and overheat. This, hardens the elastomer and diminishes the effectiveness of the seal. Aside from that, the two lips acting against the wear ring impart a measure of resistance to rotation, and that resistance requires torque to overcome--torque which could otherwise be utilized in performing useful work.
Furthermore, the typical all-purpose bearing of current construction when mounted on an axle journal, has no overhangs or other protection for the seals at the ends of the bearing, and hence the seals are exposed directly to contaminants on their air sides. Should a seal be the least bit defective, it may admit the contaminants to the interior of the bearing that it is designed to protect.
The seal of the present invention operates with considerably less torque than conventional seals of the type currently utilized with all-purpose bearings. Moreover, it establishes at least two barriers to the migration of contaminants. It further operates in conjunction with a shield that provides an overhang for excluding contaminants and even deflecting them away from the seal.